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W. A. Cobban

Publications and source records attributed to W. A. Cobban.

At least 19 recordsLinked to original sources
USGS2016

Middle Campanian ammonites and inoceramids from the Wolfe City Sand in northeastern Texas

The middle Campanian Wolfe City Sand in northeastern Texas yields a distinctive ammonite and inoceramid fauna with Patagiosites sp., Placenticeras sp., Hoplitoplacenticeras ( Hoplitoplacenticeras ) minor n. sp., Baculites mclearni Landes, 1940, Trachyscaphites spiniger (Schlüter, 1872) porchi (Adkins, 1929), Inoceramus ( Cordiceramus ) azerbaidjanensis Aliev, 1939, and I. ( Endocostea ) balticus Boehm, 1907. The last-named four species allow a direct correlation with the Baculites mclearni zone of the Western Interior of the United States. The base of this zone has been dated at 79.9 ± 3.2/79.2 ± 1.6 Ma on the basis of K/Ar determinations on biotite from a bentonite. Inoceramus azerbaidjanensis is also known from the Campanian of the U.S.S.R. in Azerbaidjan (where the species was first described), western Turkemenia, Georgia, the northern Caucasus, the Crimea, and Donbass.

Journal of Paleontology↗
USGS2016

Maastrichtian ammonites from the Hornerstown Formation in New Jersey

The base of the Paleocene Hornerstown Formation at the Inversand pit and certain other localities in New Jersey yields a diverse phosphatised fauna of Maastrichtian age, including the ammonites Pachydsicus ( Neodesmoceras) mokotibensis Collignon, 1952, Sphenodiscus lobatus (Tuomey, 1854), Baculites spp., and Eubaculites carinatus (Morton, 1834). S. lobatus is known from the older Red Bank Sand and Tinton Sand in New Jersey; the other species are known only from the basal Hornerstown. Occurrences at the Inversand pit are regarded as either reworked or remainié, although details of Cretaceous/Paleocene boundary events have been destroyed by pervasive burrowing that pipes the Hornerstown down into the underlying Navesink Formation.

Journal of Paleontology↗
USGS2016

Upper campanian (upper cretaceous) ammonites from the Marshalltown Formation-Mount laurel boundary beds in Delaware

New collections from the Marshalltown Formation and basal Mount Laurel Sand along the Chesapeake and Delaware Canal in Delaware clarify the ammonite dating of the interval. The Marshalltown Formation yields Pachydiscus ( Pachydiscus ) sp., Menuites portlocki (Sharpe, 1855) complexus (Hall and Meek, 1856), a subspecies restricted to the Baculites gregoryensis and Baculites scotti zones in the Western Interior of the United States, and Didymoceras binodosum (Kennedy and Cobban, 1993a) known only from the B. scotti zone of the Western Interior and correlatives in Arkansas and Texas. The basal part of the Mount Laurel Sand contains a complex assemblage preserved as phosphatic molds: Nostoceras ( Nostoceras ) monotuberculatum Kennedy and Cobban, 1993a, Nostoceras (N.) sp., Didymoceras platycostatum (Kennedy and Cobban, 1993b), D. stevensoni (Whitfield, 1877) (previously thought to be from the Marshalltown) and Exiteloceras jenneyi (Whitfield, 1877). The last two are index species of their eponymous zones in the Western Interior. This sequence is compatible with ammonites from the Wenonah Formation, which lies between the Marshalltown and Mount Laurel to the north and contains ammonites indicative of the Baculites scotti zone, and the fauna from higher in the Mount Laurel Sand, which includes elements of the Didymoceras cheyennense and Baculites compressus zones of the Western Interior sequence.

Journal of Paleontology↗
USGS2011

Biostratigraphic data from Upper Cretaceous formations-eastern Wyoming, central Colorado, and northeastern New Mexico

Lithological and paleontological studies of outcrops of Upper Cretaceous formations were conducted at 12 localities in eastern Wyoming, central Colorado, and northeastern New Mexico. The sequence extends upward from the top of the Mowry Shale, or age-equivalent rocks, through the Graneros Shale, Greenhorn Limestone, Carlile Shale, Niobrara Formation, Pierre Shale, and Fox Hills Sandstone, or age-equivalent formations, to the top of the Laramie Formation, or laterally equivalent formations. The strata are mainly siliciclastic and calcareous, with thicknesses ranging from about 3,300 ft in northeastern New Mexico to as much as 13,500 ft in eastern Wyoming. Deposition was mainly in marine environments and molluscan fossils of Cenomanian through Maastrichtian ages are common. Radiometric ages were determined from beds of bentonite that are associated with fossil zones. The Upper Cretaceous formations at the 12 study localities are herein divided into three informal time-stratigraphic units based on fossil content and contact relations with adjacent strata. The basal unit in most places extends from the base of the Graneros to the top of the Niobrara, generally to the horizon of the fossil Scaphites hippocrepis, and spans a period of about 14 million years. The middle unit generally extends from the top of the Niobrara to the approximate middle of the Pierre, the horizon of the fossil Baculites gregoryensis, and represents a period of about 5 million years. The upper unit includes strata between the middle of the Pierre and the top of the Upper Cretaceous Series, which is the top of the Laramie Formation or of laterally equivalent formations; it represents a period of deposition of as much as 11 million years. Comparisons of the collections of fossils from each outcrop with the complete sequence of Upper Cretaceous index fossils can indicate disconformable contacts and lacunae. Widespread disconformities have been found within the Carlile Shale and between the Carlile Shale and the Niobrara Formation. Less extensive disconformities are within the Greenhorn Formation, the Niobrara Formation, and the Pierre Shale.

Scientific Investigations Map↗
USGS2010

Outcrops, fossils, geophysical logs, and tectonic interpretations of the Upper Cretaceous Frontier Formation and contiguous strata in the Bighorn Basin, Wyoming and Montana

In the Bighorn Basin of north-central Wyoming and south-central Montana, the Frontier Formation of early Late Cretaceous age consists of siliciclastic, bentonitic, and carbonaceous beds that were deposited in marine, brackish-water, and continental environments. Most lithologic units are laterally discontinuous. The Frontier Formation conformably overlies the Mowry Shale and is conformably overlain by the Cody Shale. Molluscan fossils collected from outcrops of these formations and listed in this report are mainly of marine origin and of Cenomanian, Turonian, and Coniacian ages. The lower and thicker part of the Frontier in the Bighorn Basin is of Cenomanian age and laterally equivalent to the Belle Fourche Member of the Frontier in central Wyoming. Near the west edge of the basin, these basal strata are disconformably overlain by middle Turonian beds that are the age equivalent of the Emigrant Gap Member of the Frontier in central Wyoming. The middle Turonian beds are disconformably overlain by lower Coniacian strata. Cenomanian strata along the south and east margins of the basin are disconformably overlain by upper Turonian beds in the upper part of the Frontier, as well as in the lower part of the Cody; these are, in turn, conformably overlain by lower Coniacian strata. Thicknesses and ages of Cenomanian strata in the Bighorn Basin and adjoining regions are evidence of regional differential erosion and the presence of an uplift during the early Turonian centered in northwestern Wyoming, west of the basin, probably associated with a eustatic event. The truncated Cenomanian strata were buried by lower middle Turonian beds during a marine transgression and possibly during regional subsidence and a eustatic rise. An uplift in the late middle Turonian, centered in north-central Wyoming and possibly associated with a eustatic fall, caused the erosion of lower middle Turonian beds in southern and eastern areas of the basin as well as in an adjoining region of north-central Wyoming. Similarly, in east-central Wyoming and an adjacent area to the south, Cenomanian strata are disconformably overlain by upper middle and lower upper Turonian strata that probably reflect uplift and erosion in that region during the interim period of middle Turonian time. During later subsidence and a marine transgression, upper Turonian deposits buried Cenomanian beds in areas along the south and east margins of the Bighorn Basin and buried lower middle Turonian beds in much of northern Wyoming. Upper Turonian and lower Coniacian strata are apparently conformable in eastern and southern areas of the basin as well as near Riverton, Kaycee, and Casper in central Wyoming. Upper Turonian strata are absent on the west flank of the Bighorn Basin and in outcrops west of the basin, where middle Turonian beds are disconformably overlain by lower Coniacian beds . The conformable upper Turonian and lower Coniacian beds apparently transgressed an eroded middle Turonian surface in the region, but only Coniacian strata overlie middle Turonian beds on the west side of the basin and areas farther west. Coniacian strata onlap the truncated lower middle Turonian surface west of the basin, indicating a region that had higher elevation possibly resulting from tectonic uplift. In east-central Wyoming and an adjoining region to the south, upper middle Turonian and lower upper Turonian strata are disconformably overlain by lower and middle Coniacian beds. That region apparently was uplifted and eroded during the latest Turonian.

Montana, Wyoming↗
USGS2009

Fossils, lithologies, and geophysical logs of the Mancos Shale from core hole USGS CL-1 in Montrose County, Colorado

As part of a multidisciplinary investigation of Mancos Shale landscapes in the Gunnison Gorge National Conservation Area in Delta and Montrose Counties of western Colorado by the U.S. Geological Survey, Bureau of Land Management, and Bureau of Reclamation, a core of the Upper Cretaceous Mancos Shale was obtained from a borehole, USGS CL-1, in NE1/4 sec. 8, T. 50 N., R. 9 W. (approximately lat 38.61717 degree(s) N., long 107.90174 degree(s) W.), near the town of Olathe. Geophysical records of the borehole include resistivity, gamma ray, and density logs. The core extends between depths of 20 and 557 ft and is about 2.5 in. in diameter. It is composed of calcareous silty shale, as well as scattered beds of limestone and bentonite which were deposited mainly in offshore marine environments during the Cenomanian, Turonian, and Coniacian Stages of the Cretaceous Series. The strata were sampled and analyzed to obtain geochemical data and to identify constituent fossils. Stratigraphic units within the Mancos in the core include the following members, in ascending order: Bridge Creek Limestone (part), Fairport, Blue Hill, Juana Lopez, Montezuma Valley, and Niobrara (part). Strata herein assigned to the Bridge Creek Limestone are about 18 ft thick and consist of silty shale that contains ammonites, bivalves, and a coral of Late Cenomanian age. Strata assigned to the Fairport are about 22 ft thick and composed mainly of calcarenite-bearing, calcareous shale. Fossils in this member include ammonites and bivalves of early middle Turonian age. Overlying the Fairport is the Blue Hill Member, which is about 139 ft thick, and consists of glauconitic, shaley siltstone, and less silty shale. The Juana Lopez Member, overlying the Blue Hill, is about 138 ft thick and composed mainly of calcarenitic, silty shale. Beds in this member contain ammonites and bivalves of late middle and early late Turonian ages. Overlying the Juana Lopez is the Montezuma Valley Member, which is about 55 ft thick and consists of calcarenitic, calcareous silty shale. The Montezuma Valley Member contains ammonites and bivalves of late Turonian age. It is overlain by a lower part of the Niobrara Member of the Mancos Shale which is laterally equivalent to the Fort Hays Limestone Member and part of the overlying Smoky Hill Member of the Niobrara Formation at outcrops in central Colorado. Strata in the core comparable to the Fort Hays are about 39 ft thick and include shaley limestone and calcareous shale, which contain lower Coniacian bivalves. Strata in the core equivalent to part of the Smoky Hill are about 126 ft thick and consist mainly of calcareous silty shale which also contains lower Coniacian bivalves.

Open-File Report↗
USGS2008

Upper Cretaceous molluscan record along a transect from Virden, New Mexico, to Del Rio, Texas

Updated age assignments and new collections of molluscan fossils from lower Cenomanian through upper Campanian strata in Texas permit a much refined biostratigraphic correlation with the rocks of New Mexico and the Western Interior. Generic names of many Late Cretaceous ammonites and inoceramid bivalves from Texas are updated to permit this correlation. Strata correlated in the west-to-east transect include the lower Cenomanian Beartooth Quartzite and Sarten Sandstone of southwest New Mexico, and the Eagle Mountains Formation, Del Rio Clay, Buda Limestone, and. basal beds of the Chispa Summit, Ojinaga, and Boquillas Formations of the Texas-Mexico border area. Middle Cenomanian strata are lacking in southwestern New Mexico but are present in the lower parts of the Chispa Summit and Boquillas Formations in southwest Texas. Upper Cenomanian and lower Turonian rocks are present at many localities in New Mexico and Texas in the Mancos Shale and Chispa Summit, Ojinaga, and Boquillas Formations. Middle Turonian and younger rocks seem to be entirely nonmarine in southwestern New Mexico, but they are marine in the Rio Grande area in the Chispa. Summit, Ojinaga, and Boquillas Formations. The upper part of the Chispa Summit and Boquillas contain late Turonian fossils. Rocks of Coniacian and Santonian age are present high in the Chispa Summit, Ojinaga, and Boquillas Formations, and in the lower part of the Austin. The San Carlos, Aguja, Pen, and Austin Formations contain fossils of Campanian age. Fossils representing at least 38 Upper Cretaceous ammonite zones are present along the transect. Collections made in recent years in southwestern New Mexico and at Sierra de Cristo Rey just west of downtown El Paso, Texas, have been well treated and do not need revision. Taxonomic names and zonations published in the pre-1970 literature on the Rio Grande area of Texas have been updated. New fossil collections from the Big Bend National Park, Texas, allow for a much refined correlation in the central part of the transect in Texas. Middle Turonian-Campanian zonation in southwest Texas is based mainly on ammonites of the Family Collignoniceratidae, as opposed to the scaphitid and baculitid ammonites that are especially abundant farther north in the Western Interior.

New Mexico Geology↗
USGS2007

Outcrop descriptions and fossils from the Upper Cretaceous Frontier Formation, Wind River Basin and adjacent areas, Wyoming: Chapter 11 in Petroleum systems and geologic assessment of oil and gas resources in the Wind River Basin Province, Wyoming

The Wind River Basin of central Wyoming trends west-northwest from near the community of Alcova to near the town of Dubois (fig. 1). On the perimeter of the basin, outcrops of the Frontier Formation were examined and described during the years 1972-1975. Invertebrate fossils were collected from those outcrops during the years 1972-1996, in places with the assistance of other earth scientists (see Acknowledgments). The Frontier Formation in the Wind River Basin, ranging in thickness from 650 to 1,000 ft thick, consists mainly of sandstone, siltstone, shale, and bentonite of early Late Cretaceous age. The Frontier conformably overlies the Mowry Shale and is conformably overlain by the Cody Shale. A basal unit of the Cody, a sequence of marine noncalcareous shale, is named the Sage Breaks Member. The Frontier consists of two or three members, separated by disconformities; in ascending order, the Belle Fourche, Emigrant Gap, and Wall Creek. At several localities, the Emigrant Gap Member is missing. The formation was deposited mainly in marine environments, although nonmarine beds are conspicuous in the western part of the basin. Strata of the Frontier record a succession of marine regressions and transgressions. Molluscan fossils from the marine beds were identified and related to the chronostratigraphic chart shown in figure 2. The absolute ages on the chart were determined and supplied by J.D. Obradovich (Cobban and others, 2006). In this region, the Belle Fourche is of Cenomanian age, the Emigrant Gap is of early middle Turonian age, and the Wall Creek is of late Turonian and early Coniacian ages. The main purpose of this report is to present biostratigraphic information from studies of the Frontier Formation in the Wind River Basin that could be useful for future stratigraphic investigations of the formation throughout Wyoming. Locations of outcrop sections and associated fossil collections are depicted on accompanying maps and aerial photographs. Graphic descriptions of strata in the outcrops and identifications of fossils from nearby localities also are presented. Those fossils named on the graphic sections commonly have the most restricted time-spans. Fossils collected near the outcrops studied are not always named on the enclosed graphic sections because (1) the specimens are less useful for dating the enclosing beds, (2) the specimens are duplicates, or (3) the specimens could not be related to specific strata in the sections. The names, locations, and members of the outcrop sections and the approximate ages of the constituent strata are summarized in table 1. The index maps used to show locations of outcrop sections and fossil collections are from scanned versions of U.S. Geological Survey topographic maps of various scales and were obtained from TerraServer®. The portion of each map used depended on the areal distribution of the localities involved. The named quadrangles used for locality descriptions, however, all refer to 7½-minute, 1:24,000-scale quadrangles (for example, “Alcova”). The aerial photographs also are from TerraServer®; http://www.terraserver.com/.

Wyoming↗
USGS2002

Regional stratigraphic cross sections of Cretaceous rocks from east-central Arizona to the Oklahoma Panhandle

Sedimentary rocks of Cretaceous age along Transect DD'' in eastern Arizona, northern New Mexico, southern Colorado, and western Oklahoma consist mainly of sandstone, siltstone, shale, limestone, and bentonite. They accumulated as sediments in continental, nearshore marine, and offshore marine environments on the west side of a north-trending epicontinental sea. The rocks record intermittent deposition and erosion as well as regional and local subsidence and uplift possibly beginning in Aptian time (about 121-112 Ma) and occurring in Albian through Maastrichtian time (about 112-65.4 Ma). Most of the Lower Cretaceous (Berriasian through Aptian, 142-112 Ma) in this transect is represented by a basal unconformity. The Cretaceous rocks and unconformities along the transect are depicted on the attached lithostratigraphic cross sections (sheets 1 and 2); one extending from the Mogollon Rim in eastern Arizona to Pagosa Springs in southwestern Colorado and the other from Pagosa Springs, Colorado, to Kenton in western Oklahoma. The same rocks and unconformities are also represented on the attached chronostratigraphic profile (sheet 3), which was prepared mainly from surface and subsurface data shown on the lithostratigraphic cross sections.

Arizona, New Mexico, Oklahoma↗
USGS1998

40Ar/39Ar age of the Manson impact structure, Iowa, and correlative impact ejecta in the Crow Creek member of the Pierre Shale (Upper Cretaceous), South Dakota and Nebraska

A set of 34 laser total-fusion 40 Ar/ 39 Ar analyses of sanidine from a melt layer in crater-fill deposits of the Manson impact structure in Iowa has a weighted-mean age of 74.1 ± 0.1 Ma. This age is about 9.0 m.y. older than 40 Ar/ 39 Ar ages of shocked microcline from the Manson impact structure reported previously by others. The 74.1 Ma age of the sanidine, which is a melt product of Precambrian microcline clasts, indicates that the Manson impact structure played no part in the Cretaceous-Tertiary (K-T) mass extinction at 64.5 Ma. Moreover, incremental-heating 40 Ar/ 39 Ar ages of the sanidine show that it is essentially free of excess 40 Ar and has not been influenced by postcrystallization heating or alteration. An age spectrum of the matrix of the melt layer shows effects of 39 Ar recoil, including older ages in the low-temperature increments and younger ages in the high-temperature increments. At 17 places in eastern South Dakota and Nebraska, shocked quartz and feldspar grains are concentrated in the lower part of the Crow Creek Member of the Pierre Shale (Upper Cretaceous). The grains are largest (3.2 mm) in southeastern South Dakota and decrease in size (0.45 mm) to the northwest, consistent with the idea that the Manson impact structure was their source. The ubiquitous presence of shocked grains concentrated in a thin calcarenite at the base of the Crow Creek Member suggests it is an event bed recording an instant of geologic time. Ammonites below and above the Crow Creek Member limit its age to the zone of Didymoceras nebrascense of earliest late Campanian age. Plagioclase from a bentonite bed in this zone in Colorado has a 40 Ar/ 39 Ar age of 74.1 ± 0.1 Ma commensurate with our sanidine age of 74.1 Ma for the Manson impact structure. 40 Ar/ 39 Ar ages of bentonite beds below and above the Crow Creek are consistent with our 74.1 ± 0.1 Ma age for the Manson impact structure and limit its age to the interval ±74.5 0.1 to 73.8 ± 0.1 Ma. Recently, two origins for the Crow Creek have been proposed—eastward transgression of the Late Cretaceous sea and a Manson impact-triggered tsunami. We conclude that most data are in accord with an impact origin for the Crow Creek Member and are at odds with the marine transgression hypothesis.

Iowa, Nebraska, South Dakota↗
USGS1994

Cretaceous rocks from southwestern Montana to southwestern Minnesota, northern Rocky Mountains, and Great Plains

In Montana, Wyoming, North and South Dakota, and Minnesota, Cretaceous strata are preserved in the asymmetric Western Interior foreland basin. More than 5,200 m (17,000 ft) of Cretaceous strata are present in southwestern Montana, less than 300 m (1,000 ft) in eastern South Dakota. The asymmetry resulted from varying rates of subsidence due to tectonic and sediment loading. The strata consist primarily of sandstone, siltstone, mudstone, and shale. Conglomerate is locally abundant along the western margin, whereas carbonate is present in most areas of the eastern shelf. Sediment was deposited in both marine and nonmarine environments as the shoreline fluctuated during major tectonic and eustatic cycles. A discussion of Cretaceous strata from southwestern to east-central Montana, the Black Hills, eastern South Dakota, and southwestern Minnesota shows regional stratigraphy and facies relations, sequence, boundaries, and biostratigraphic and radiometric correlations. The thick Cretaceous strata in southwestern Montana typify nonmarine facies of the rapidly subsiding westernmost part of the basin. These strata include more than 3,000 m (10,000 ft) of synorogenic conglomerate of the Upper Cretaceous part of the Beaverhead Group. West of the Madison Range, sequence boundaries bracket the Kootenai (Aptian and Albian), the Blackleaf (Albian and Cenomanian), and the Frontier Formations (Cenomanian and Turonian); sequence boundaries are difficult to recognize because the rocks are dominantly non-marine. Cretaceous strata in east-central Montana (about 1,371 m; 4,500 ft thick) lie at the approximate depositional axis of the basin and are mostly marine terrigenous rocks. Chert-pebble zones in these rocks reflect stratigraphic breaks that may correlate with sequence boundaries to the east and west. Cretaceous rocks of the Black Hills region consist of a predominantly marine clastic sequence averaging approximately 1,524 m (5,000 ft) thick. The Cretaceous System in eastern South Dakota (457 to 610 m; 1,500 to 2,000 ft thick) consists of a marine shelf sequence dominated by shale and limestone. Major sequence boundaries in South Dakota are at the base of the Lower Cretaceous Lakota Formation, Fall River Sandstone, and Muddy Sandstone, and bracket the Upper Cretaceous Niobrara Formation.

Book chapter↗
USGS1993

The Manson Impact Structure: 40Ar/39Ar age and its distal impact ejecta in the Pierre Shale in southeastern South Dakota

The 40 Ar/ 39 Ar ages of a sanidine clast from a melt-matrix breccia of the Manson, Iowa, impact structure (MIS) indicate that the MIS formed 73.8 ± 0.3 million years ago (Ma) and is not coincident with the Cretaceous-Tertiary boundary (64.43 ± 0.05 Ma). The MIS sanidine is 9 million years older than 40 Ar/ 39 Ar age spectra of MIS shock-metamorphosed microcline and melt-matrix breccia interpreted earlier to be 64 to 65 Ma. Grains of shock-metamorphosed quartz, feldspar, and zircon were found in the Crow Creek Member (upper Campanian) at a biostratigraphic level constrained by radiometric ages in the Pierre Shale of South Dakota that are consistent with the 40 Ar/ 39 Ar age of 73.8 ± 0.3 Ma for MIS reported herein.

South Dakota↗
USGS1992

Campanian ammonites from the Upper Cretaceous Gober Chalk of Lamar County, Texas

The Roxton Limestone Member at the top of the Gober Chalk in northeast Texas yields a rich fauna, dominated by Baculites haresi Reeside, 1927, and Inoceramus balticus Boehm, 1909, with sparse occurrences of pachydiscus cf. P. paulsoni (Young, 1963), Anapachydiscus sp.juv., Placenticeras placenta (DeKay, 1828), Hoplitoplacenticeras aff. H. plasticum (Paulcke, 1907), Menabites (Delawarella) delawarensis (Morton, 1830), M.(D.) danei (Young, 1963), M.(D.) aff. M.(D.) vanuxemi (Morton, 1830), Submortoniceras vandalinaense Young, 1963, Submortoniceras sp., Eubostrychoceras sp., and Scaphites hippocrepis (DeKay, 1828) III. The presence of S. hippocrepis III suggests a late early Campanian age assignment for the fauna. The assemblage includes species known from the Western Interior, Gulf Coast, Atlantic seaboard, and western Europe. -Authors

Journal of Paleontology↗